1. Field of the Invention
The present invention relates to vehicle hydraulic steering damper apparatus suitable for use in a steering system of a two-wheeled vehicle, and to a vehicle incorporating the described apparatus.
2. Description of the Background Art
Conventionally, a number of steering damper designs are known for use on two-wheeled vehicles. For example, a steering damper arranged above a head pipe provided at a front end of a vehicle body frame has previously been disclosed (See, for example, Japanese Patent Laid-Open No. 2003-81172).
FIG. 9 of the drawings in the present invention disclosure is a reproduction of FIG. 2 of Japanese Patent Laid-Open No. 2003-81172, included herein for discussion purposes. However, the reference numerals in FIG. 9 hereof have been changed from the original numbers used in the reference.
In the prior art structure depicted in FIG. 9, a steering damper 200 is a hydraulic attenuator arranged between a top bridge 201, which is part of a pivotally movable steering structure, and a substantially rigid head portion 203 attached to and located forward of the vehicle body frame 202.
The steering damper 200 of FIG. 9 has a body portion 204 and a lid 205, which cooperate to define a casing. At this time, the body portion 204 and the lid 205 are jointly fastened together.
A rear portion of the steering damper 200 is connected to a boss 207, which protrudes upwardly on the upper surface of the head portion 203 of the vehicle body frame 202. The steering damper 200 is attached to the boss 207 by a bolt 206.
A steering nut 208 fastens the upper end of a steering shaft 211, located inside a head pipe 209, to the top bridge 201. Also, the steering nut 208 surrounds the lower end of a pivot shaft 212, which is a rotatable shaft of the steering damper 200, and which is fixedly connected to the steering shaft 211. The pivot shaft 212 is also connected to the top bridge 201 via the steering nut 208.
In other words, the pivot shaft 212 and the steering shaft 211 are connected to one another, and rotate integrally together via the top bridge 201.
In this respect, reference numeral 213 designates a bottom bridge; 214, a fuel tank; and 215, a turning angle sensor.
When the vehicle receives an external force from a road surface while it is traveling, the steering damper 200 detects a turning angle of the steering shaft 211 with the turning angle sensor 215, which rotates integrally with the pivot shaft 212. The damper 200 is operable to absorb the external force from the road surface by outputting a signal to a control apparatus.
In the structure of the steering damper 200 of the Japanese Patent Laid-Open No. 2003-81172, however, although the pivot shaft 212 is directly fitted in the steering shaft 211, there is a problem that in order to accurately determine the relative positions of the pivot shaft 212 and the steering shaft 211, it is necessary to use enhanced precision parts, and thus it is difficult and expensive to manufacture.
Also, the pivot shaft 212 and the top bridge 201 can be connected together through the use of an adjustment mechanism, such as a coupling arm and a spherical bearing incorporating an eccentric collar. However, there is a problem in that the structure of the spherical bearing incorporating the eccentric collar is complicated, resulting in increased maintenance expenses.
A steering damper apparatus to be installed to a vehicle such as a motorcycle has been proposed in which, during pivotal motion of a movable partition wall for partitioning an oil chamber within a housing into two parts, a damping force is generated by circulating hydraulic fluid between these two oil chambers. The apparatus comprises a shaft for pivotally supporting the movable partition wall with respect to the housing, while coupling the base of the movable partition wall in a fixed state. The housing and shaft are arranged above the head pipe. The rear portion of the housing is housed within a concave portion formed at the front end portion of the fuel tank. See, for example, Japanese Patent Laid-Open No. 2003-104269, with special reference to page 2 and FIG. 2 thereof.
In the steering damper apparatus specified in Japanese Patent Laid-Open No. 2003-104269, the steering damper includes the housing, the shaft and the like, and a connected portion between this steering damper and the steering system members are exposed to weathering and to the elements on the outside thereof.
An additional concern is related to the placement of the damper on the vehicle. The steering damper apparatus is arranged to be centered in the front part of the vehicle body above the head pipe. This is one of the most conspicuous places on the vehicle, and the outside appearance of this portion can be considered to be made unattractive by placement of the steering damper in this location.